A series of saline soil-related problems, including salt expansion and collapse, frost heave and thaw settlement, threaten the safety of the road traffic and the built infrastructure in cold regions. This article presents a comprehensive review of the physical and mechanical properties, salt migration mechanisms of saline soil in cold environment, and the countermeasures in practice. It is organized as follows: (1) The basic physical characteristics; (2) The strength criteria and constitutive models; (3) Water and salt migration characteristics and mechanisms; and (4) Countermeasures of frost heave and salt expansion. The review provides a holistic perspective for recent progress in the strength characteristics, mechanisms of frost heave and salt expansion, engineering countermeasures of saline soil in cold regions. Future research is proposed on issues such as the effects of salt erosion on concrete and salt corrosion of metal under the joint action of evaporation and freeze-thaw cycles.

Soil freeze-thaw process is closely related to surface energy budget, hydrological activity, and terrestrial ecosystems. In this study, two numerical experiments (including and excluding soil freeze-thaw process) were designed to examine the effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region in the Northern Hemisphere based on the state-of-the-art Community Earth System Model version 1.0.5. Results show that in response to soil freeze-thaw process, the area averaged soil temperature in the shallow layer (0.0175-0.0451 m) decreases by 0.35 ℃ in the TP (Tibetan Plateau), 0.69 ℃ in CES (Central and Eastern Siberia), and 0.6 ℃ in NA (North America) during summer, and increases by 1.93 ℃ in the TP, 2.28 ℃ in CES and 1.61 ℃ in NA during winter, respectively. Meanwhile, in response to soil freeze-thaw process, the area averaged soil liquid water content increases in summer and decrease in winter. For surface heat flux components, the ground heat flux is most significantly affected by the freeze-thaw process in both summer and winter, followed by sensible heat flux and latent heat flux in summer. In the TP area, the ground heat flux increases by 2.82 W/m² (28.5%) in summer and decreases by 3.63 W/m² (40%) in winter. Meanwhile, in CES, the ground heat flux increases by 1.89 W/m² (11.3%) in summer and decreases by 1.41 W/m² (18.6%) in winter. The heat fluxes in the Tibetan Plateau are more susceptible to the freeze-thaw process compared with the high-latitude frozen soil regions. Soil freeze-thaw process can induce significant warming in the Tibetan Plateau in winter. Also, this process induces significant cooling in high-latitude regions in summer. The frozen ground can prevent soil liquid water from infiltrating to deep soil layers at the beginning of thawing; however, as the frozen ground thaws continuously, the infiltration of the liquid water increases and the deep soil can store water like a sponge, accompanied by decreasing surface runoff. The influence of the soil freeze-thaw process on surface hydrologic and thermal fluxes varies seasonally and spatially.

Taking advantage of heat absorbing and releasing capability of phase change material (PCM), Paraffin wax-based concrete was prepared to assess its automatic temperature control performance. The mechanical properties of PCM concrete with eight different Paraffin wax contents were tested by the cube compression test and four-point bending test. The more Paraffin wax incorporated, the greater loss of the compressive strength and bending strength. Based on the mechanical results, four contents of Paraffin wax were chosen for studying PCM concrete's thermal properties, including thermal conductivity, thermal diffusivity, specific heat capacity, thermal expansion coefficient and adiabatic temperature rise. When the Paraffin wax content increases from 10% to 20%, the thermal conductivity and the thermal diffusivity decrease from 7.31 kJ/(m·h·°C) to 7.10 kJ/(m·h·°C) and from 3.03×10^-3 m²/h to 2.44×10^-3 m²/h, respectively. Meanwhile the specific heat capacity and thermal expansion coefficient rise from 5.38×10^-1 kJ/(kg·°C) to 5.76×10^-1 kJ/(kg·°C) and from 9.63×10^-6/°C to 14.02×10^-6/°C, respectively. The adiabatic temperature rise is found to decrease with an increasing Paraffin wax content. Considering both the mechanical and thermal properties, 15% of Paraffin wax was elected for the mass concrete model test, and the model test results confirm the effect of Paraffin wax in automatic mass concrete temperature control.

The revegetation protection system (VPS) on the edge of the Tengger Desert can be referred to as a successful model of sand control technology in China and even the world, and there has been a substantial amount of research on revegetation stability. However, it is unclear how meso- and micro-scale revegetation activity has responded to climatic change over the past decades. To evaluate the relative influence of climatic variables on revegetation activities in a restored desert ecosystem, we analysed the trend of revegetation change from 2002 to 2015 using a satellite-derived normalized difference vegetation index (NDVI) dataset. The time series of the NDVI data were decomposed into trend, seasonal, and random components using a segmented regression method. The results of the segmented regression model indicate a changing trend in the NDVI in the VPS, changing from a decrease (-7×10^-3/month) before 2005 to an increase (0.3×10^-3/month) after 2005. We found that precipitation was the most important climatic factor influencing the growing season NDVI (P <0.05), while vegetation growth sensitivity to water and heat varied significantly in different seasons. In the case of precipitation reduction and warming in the study area, the NDVI of the VPS could still maintain an overall slow upward trend (0.04×10^-3/month), indicating that the ecosystem is sustainable. Our findings suggest that the VPS has been successful in maintaining stability and sustainability under current climate change conditions and that it is possible to introduce the VPS in similar areas as a template for resistance to sand and drought hazards.

To reveal the characteristics of evapotranspiration and environmental control factors of typical underlying surfaces (alpine wetland and alpine meadow) on the Qinghai-Tibetan Plateau, a comprehensive study was performed via in situ observations and remote sensing data in the growing season and non-growing season. Evapotranspiration was positively correlated with precipitation, the decoupling coefficient, and the enhanced vegetation index, but was energy-limited and mainly controlled by the vapor pressure deficit and solar radiation at an annual scale and growing season scale, respectively. Compared with the non-growing season, monthly evapotranspiration, equilibrium evaporation, and decoupling coefficient were greater in the growing season due to lower vegetation resistance and considerable precipitation. However, these factors were restricted in the alpine meadow. The decoupling factor was more sensitive to changes of conductance in the alpine wetland. This study is of great significance for understanding hydro-meteorological processes on the Qinghai-Tibetan Plateau.

Based on the measurement of L-band ground-based microwave radiometer (ELBARA-III type) in the Qinghai-Tibet Plateau and the \tau -\omega radiative transfer model, this research evaluated the effects of four soil dielectric models, i.e., Wang-Schmugge, Mironov, Dobson, and Four-phase, on the L-band microwave brightness temperature simulation and soil moisture retrieval. The results show that with the same vegetation and roughness parameterization scheme, the four soil dielectric models display obvious differences in microwave brightness temperature simulation. When the soil moisture is less than 0.23 m³/m³, the simulated microwave brightness temperature in Wang-Schmugge model is significantly different from that of the other three models, with maximum differences of horizontal polarization and vertical polarization reaching 8.0 K and 4.4 K, respectively; when the soil moisture is greater than 0.23 m³/m³, the simulated microwave brightness temperature of Four-phase significantly exceeds that of the other three models; when the soil moisture is saturated, maximum differences in simulated microwave brightness temperature with horizontal polarization and vertical polarization are 6.1 K and 4.8 K respectively, and the four soil dielectric models are more variable in the microwave brightness temperature simulation with horizontal polarization than that with vertical polarization. As for the soil moisture retrieval based on the four dielectric models, the comparison study shows that, under the condition of horizontal polarization, Wang-Schmugge model can reduce the degree of retrieved soil moisture underestimating the observed soil moisture more effectively than other parameterization schemes, while under the condition of vertical polarization, the Mironov model can reduce the degree of retrieved soil moisture overestimating the observed soil moisture. Finally, based on the Wang-Schmugge model and FengYun-3C observation data, the spatial distribution of soil moisture in the study area is retrieved.